Yes, the lumberyard can order them. While you are there, go over the plan with them and insure that what you propose is adequate. I am by no means telling you what to use for a ridge. Sounds like in reading your other post that you may have a real tough time cutting the rafters correctly. Figuring the length is carpentry 101. It would benefit you to hire someone to at least help with layour, cutting, and assembly.

Thanks. I already went to the lumber yard and they are the ones that suggested the 2x12x20 ridge board with the 2x12 rafters. Which sounds like that is wrong. They also told me i would need 16 footers for the length.